1. Field of the Invention
The present invention relates to an asynchronous transfer mode (ATM) switch. More particularly, it relates to an ATM switch, which may be constituted by LSIs, each having a small number of contacting terminals, so that a compact ATM switch can be obtained.
2. Description of the Related Art
Transmission path interface circuits or subscriber line interface circuits in an ATM switch perform various kinds of processing for passing cells. The switch, which performs such various kinds of processing, is generally constituted with a plurality of large sized LSIs.
FIG. 12 shows a concept of a structure for a device, which performs cell processing. A plurality of large sized LSI-1 to LSI-n, each of which performs a corresponding processing on each of a plurality of processing steps, are provided in a cascade form on a cell highway (cell HW), on which usual cells are passed.
An interface circuit, not shown in the diagram, converts the usual cells on the cell HW to parallel signals in order to decrease the speed of cell transmission. The converted cells pass through each of the LSI-1 to LSI-n, and are subjected to the corresponding processing therein.
The plurality of LSI-1 to LSI-n are connected to and controlled by a micro processor 10 via a processor bus PBS. For example, a case where a transmission speed of the usual cells is 10 Mbps, address signals are transmitted in parallel with 16 bits, and data are transmitted in parallel with 32 bits, will be now considered. A processor bus PBS, which is constituted with several ten control lines, connects each of the plurality of LSI-1 to LSI-n to the micro processor 10.
Further, each of the plurality of LSI-1 to LSI-n is connected to the cell HW. If the switch is made more compact, the number of contact terminals for LSIs should be problem, as high integration of LSIs is more progressed. Since number of contact terminals for an LSI or a space for providing the contact terminals on a chip of the LSI is limited, there is a limitation in making the switch compact.
The number of contact terminals becomes larger, the more the appearance of the LSI becomes larger, thus it becomes difficult to make the switch compact.
Taking a LSI having a size of 5 by 5 square centimeters as an example, it is required to provide 304 pieces of contact pins including electrical source lines on four sides of the LSI. In this case, the pitch width between pins becomes 0.3 to 0.5 mm.
Therefore, it becomes important to reduce the number of contact terminals when designing a switch device with the use of LSIs having high density. The number of contact terminals of LSIs for use in an ATM switch, becomes large, because of input and output terminals for the converted parallel cells on the cell HW and the processor bus PBS. That causes a problem on making the switch compact.